CN101038943A

CN101038943A - Method for preparation of a-b orientated ZnO nanometer linear array

Info

Publication number: CN101038943A
Application number: CNA2006100226709A
Authority: CN
Inventors: 戴丽萍; 邓宏
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2006-12-27
Filing date: 2006-12-27
Publication date: 2007-09-19
Anticipated expiration: 2026-12-27
Also published as: CN100428502C

Abstract

The invention provides a method for preparing ZnO nano line array in a-b orientation which belongs to electronic material technical field, relates to wide bond gap semiconductor ZnO luminescent material, especially relates to a method for preparing ZnO nano line array. The invention uses chemical vapor deposition technique, and employs pure ZnO powder as evaporation source and sapphire Al2O3 (1120) as substrate, and controls the temperature of the evaporation source to be no less than the thermal decomposition temperature of the ZnO powder and the temperature of the substrate to be no less than 750 DEG C. and vacuum degree at 200 to 300 torr, and employs Ar gas as transmission gas with gas flow rate of 35 sccm. In this manner, the ZnO powder is heated to decompose into Zn and O, and then by Ar gas transmission, the ZnO nano line array in a-b orientation is deposited on the substrate. The invention employs current chemical vapor deposition technique, and can easily prepare the ZnO nano line array in a-b orientation which has excellent uv sensitive character and quick light response speed.

Description

Preparation method of a-b oriented ZnO nanowire array

Technical Field

The invention belongs to the technical field of electronic materials, relates to a wide bandgap semiconductor ZnO luminescent material, and particularly relates to a preparation method of a ZnO nanowire array.

Technical Field

In recent years, ZnO has a large exciton confinement energy (60mev), and can obtain highly efficient ultraviolet light emission at room temperature, and thus has become a hot point of research behind GaN materials. Wherein the ZnO nanowire array system is expected to be used as a next-generation nano photoelectric device. The first concern is that the ZnO nanowire array with high orientation can be used as a natural laser resonant cavity, can generate ultraviolet laser when being excited, and has an extremely low light excitation threshold of 40kW/cm²(the thin film material is 300kW/cm²～4MW/cm²) Chemical activity and one-dimensional nano structure, so that the ZnO nanowire becomes one of ideal materials for manufacturing the ultraviolet nano laser; meanwhile, the ZnO nanowire array has high brightness and good luminescence stability, the electron field emission performance of the ZnO nanowire array can meet the brightness requirement of a flat panel display device, and the ZnO nanowire array is a potential flat panel display luminescent material; the ZnO nanowire array has good ultraviolet sensitivity, so the ZnO nanowire array can be used for manufacturing high-sensitivity ultraviolet detectors and photoswitches; in addition, the ZnO nanowire array can also be used for manufacturing sensors and storage devices, nano resonance tunnel devices, field effect transistors and the like, and has wide application prospects in the fields of aerospace, information communication and the like.

At present, many methods are available for preparing ZnO nanowires, such as vapor transport method, Chemical Vapor Deposition (CVD) method, pulsed laser high-temperature evaporation method, electrodeposition method, sol-gel method, hydrothermal method, template limitation method and microemulsion method.

In the preparation of ZnO nanowire materials, one of the most critical problems is the preparation of ZnO nanowires with directional growth. Most of the reported preparation methods obtain a c-axis preferred orientation ZnO nano array; however, no ZnO nanowire array with significant a-b orientation, i.e., a ZnO nanowire array with C-axis parallel to the substrate growth, has been reported yet. And after photoelectric property tests, the a-b oriented ZnO nanowire array is found to have strong ultraviolet light sensitivity (superior to a c-axis oriented ZnO nanowire array), and particularly, the a-b oriented ZnO nanowire array is a very favorable factor for being used as a photoelectric device with high photoresponse speed (less than 50 mu s).

Disclosure of Invention

The invention adopts the chemical vapor deposition technology to prepare the ZnO nanowire array with a-b orientation. The vapor deposition method makes use of high-temperature physical evaporation or vapor phase reaction of organic metal compounds, and makes reactants deposit on a low-temperature substrate and grow into a one-dimensional structure through gas transmission. The growth direction and the size of the ZnO nanowire array have better controllability, the chemical vapor deposition technology has high deposition rate, chemical components are easy to control, formed crystal defects are less, and the ZnO nanowire array has the high-temperature characteristic suitable for nanowire growth.

The invention adopts chemical vapor deposition technology, as shown in figure 1, pure ZnO powder is used as an evaporation source, and sapphire Al is adopted₂O₃As a substrate, controlling the temperature of an evaporation source to be not lower than the thermal decomposition temperature of ZnO powder, controlling the temperature of the substrate to be not lower than 750 ℃, controlling the vacuum degree to be 200-300 torr, adopting Ar gas as transmission gas with the flow rate of 35sccm to ensure that the ZnO powder is heated and decomposed into Zn and O, and then depositing and growing an a-b oriented ZnO nanowire array on the substrate through argon transmission₂O₃The substrate is Al₂O₃(1120)。

The technical scheme of the invention needs to be explained as follows:

1. the key point of the invention

The invention adopts sapphire Al₂O₃(1120) ZnO nanowire arrays (sample 1 in FIG. 2 (a)) were prepared on substrates, using sapphire Al for comparison₂O₃(0001) An array of ZnO nanowires obtained from a substrate (as sample 2 in fig. 2 (a)). The morphology and structure of both samples are shown in fig. 2(b) and (c). When sapphire Al is used, as shown in FIG. 2(a)₂O₃(0001) Sample 2 only showed the (002) peak when it was on the substrate; while sapphire Al is used₂O₃(1120) When the substrate is used, the ZnO (002) peak of sample 1 is very small and almost disappears, and the (100) peak and the (110) peak are both very strong, indicating that the selection of the substrate is the most important factor for the oriented growth of the nanowire.

2. Technical conditions of the invention

The temperature of the source is very important to be well controlled, the proper decomposition speed of the source must be ensured, and the over-high or over-low source temperature is not favorable for the growth of the ZnO nanowire.

When growing ZnO nano-wires, a certain substrate temperature must be ensured, and when other conditions (such as reactor volume, oxygen partial pressure and the like) are the same, the higher the substrate temperature is, the larger the vapor pressure is, the larger the dimension of the prepared ZnO nano-wires is, and the more dense the ZnO nano-wires are arranged. The dimension of the ZnO nanowires increases with increasing substrate temperature.

Under the condition of certain raw materials and temperature, the gas phase partial pressure in the reactor directly influences the appearance of the product. The vessel size, feedstock usage, gas flow rate and type all affect the gas saturation in the reactor.

The argon is introduced into the reaction system, and the control of the gas flow and the deposition time are also very critical factors. If the air flow is too small or the deposition time is too short, the nanowires cannot be obtained, and if the air flow is too large, the nanowires are unbalanced in development. And the nanowires with good growth can be obtained by proper air flow and deposition time.

3. Performance characteristics of the invention

FIG. 3 is an I-V curve of a typical sample of ZnO nanowire arrays with a-b orientation prepared using the present invention. And the Au interdigital electrode and the ZnO nanowire array form ohmic contact. The dark current of the ZnO nanowire array is 8 muA at a voltage of 5V, the bright current of the ZnO nanowire array is 248.2 muA when the ZnO nanowire array is irradiated by ultraviolet light with 256nm, wherein the photoproduction current is 240.2 muA, and the a-b oriented ZnO nanowire array has excellent ultraviolet sensitivity.

The sample was exposed to a constant voltage of 5V and the sample was illuminated with the same 256nm uv lamp, and the current change of the sample was automatically recorded by the XY recorder, and fig. 4 shows its stable uv response, where it can be seen that the current rises from 8 μ a to 217.3 μ a in a time of 50 μ s, and when the uv lamp was turned off, the current drops from 248 μ a to 23.7 μ a in a time of 20 μ s, indicating that the a-b axis oriented ZnO nanowire array grown on sapphire has a rapid response to uv light.

And (3) irradiating the sample by using a spectrophotometer as a light source, and testing the light responsivity of the sample. Fig. 5 is a photoresponse curve of a typical sample, with inset SEM images of ZnO nanowires. In the range of 250nm-354nm, the light responsivity of the nanowire is increased along with the increase of the wavelength of a light source, and the light responsivity of the ZnO nanowire is maximum and is 0.56A/W when the wavelength is 354 nm. The responsivity of the sample then began to drop, and when the wavelength was greater than 450nm, the responsivity dropped to 0.14A/W. Fig. 4 shows that the absorption band of the ZnO nanowire has a more obvious "blue shift" phenomenon than that of a typical ZnO thin film sample.

The invention has the beneficial effects that:

the invention utilizes the existing chemical vapor deposition technology, adopts ZnO powder as an evaporation source and adopts sapphire Al₂O₃(1120) As a substrate, a ZnO nanowire array with a-b orientation is conveniently prepared, and the obtained ZnO nanowire array with the a-b orientation has excellent ultraviolet light sensitivity and high photoresponse speed.

Drawings

FIG. 1 is a schematic flow chart of a method for preparing a-b oriented ZnO nanowire array.

Figure 2(a) is an XRD pattern of two samples, wherein: sample 1 was sapphire Al₂O₃(1120) ZnO nanowire arrays (i.e., a-b oriented ZnO nanowire array prepared by the invention) are prepared on a substrate, and sample 2 is sapphire Al₂O₃(0001) A ZnO nanowire array obtained from a substrate (namely the existing c-axis oriented ZnO nanowire array); (b) is SEM image of ZnO nanowire array grown on sapphire (1120) substrate; (c) is SEM image of ZnO nanowire array grown on sapphire (0001) substrate.

FIG. 3 is an I-V curve of an a-b oriented ZnO nanowire array prepared by the invention under a bias voltage of-5V to 5V.

FIG. 4 is an ultraviolet response spectrum of an a-b oriented ZnO nanowire array under 5V bias and 256nm ultraviolet irradiation.

FIG. 5 is a photo-response spectrum of an a-b oriented ZnO nanowire array prepared by the present invention.

Detailed Description

The ZnO nanowire is prepared by using a dual-temperature-zone CVD system. The whole system can be divided into an air path part, a growth chamber and a control part.

The specific implementation steps are as follows:

1. preparation of an Evaporation Source

In the invention, analytically pure ZnO powder produced by chemical reagent research institute in Tianjin is used as an evaporation source.

2. Sapphire Al₂O₃(1120) Cleaning the substrate:

1) scrubbing;

2) soaking: washing with potassium dichromate solution and deionized water;

3) ultrasonic cleaning 1: in deionized water, for 5-10 minutes twice;

4) ultrasonic cleaning 2: in acetone, for 5-10 minutes twice;

5) ultrasonic cleaning 3: in absolute ethyl alcohol, for 5-10 minutes twice;

6) drying;

7) and (5) standby.

3. CVD synthesis of zinc oxide nanowires

The high-temperature thermal decomposition reaction by chemical vapor deposition has the following reaction equation:

Zn(Vapor)+O→ZnO(nanowire)

the specific operation steps are as follows:

1) the evaporation source and the substrate are placed in a reaction chamber of a CVD system. Putting ZnO powder into an alumina boat, and putting sapphire Al₂O₃(1120) The substrate is placed 10-15cm downstream of the gas path of the ZnO source.

2) Opening a vacuum pump, vacuumizing the system, and keeping the vacuum of 200&300 torr in the alumina furnace tube;

3) adjusting a temperature controller, wherein the temperature rise rate of a furnace tube is 20 ℃/min, so that ZnO powder is decomposed at the temperature of 1350 ℃, and the temperature of the substrate is stabilized at a set growth temperature of 750 ℃;

4) high purity Ar (99.99%) was used as a carrier gas, a main valve for transporting the gas was opened, a gas flow meter was opened, and the flow rate value was set to 35 sccm. Simultaneously opening a valve connected with the furnace tube to enable the transmission gas to enter the furnace tube;

5) the deposition time is 30 minutes, after the deposition is finished, the heating is stopped, the gas valve is closed, the gas flowmeter is adjusted to enable the flow rate to be zero, the furnace tube valve is closed, and the vacuum pump is closed; and taking out the sample after the temperature of the furnace tube is reduced to the room temperature, and drying to obtain the a-b oriented ZnO nanowire array.

Claims

1. A method for preparing ZnO nanowire array with a-b orientation adopts chemical vapor deposition technology, pure ZnO powder is used as an evaporation source, and sapphire Al is used₂O₃As a substrate, controlling the temperature of an evaporation source to be not lower than the thermal decomposition temperature of ZnO powder, controlling the temperature of the substrate to be not lower than 750 ℃, controlling the vacuum degree to be 200-300 torr, adopting Ar gas as transmission gas with the flow rate of 35sccm to ensure that the ZnO powder is heated and decomposed into Zn and O, and then depositing and growing an a-b oriented ZnO nanowire array on the substrate through argon transmission₂O₃The substrate is Al₂O₃(1120)。